FIG. 1 depicts a conventional magnetic element 10, which is a conventional magnetic tunneling junction (MTJ). Such a conventional MTJ 10 can be used in magnetic recording such as for a hard disk drive (HDD) as well as in other applications. In some applications, such as in a HDD, the magnetization state of the conventional MTJ 10 may be changed by applying an external field, for example in a recording head (not shown). The magnetization state of the conventional MTJ 10 may also be changed using the spin transfer effect, for example in applications such as microwave generators.
The conventional MTJ 10 typically resides on a substrate (not shown), uses seed layer(s) 11 and includes a conventional antiferromagnetic (AFM) layer 12, a conventional pinned layer 14, a conventional barrier layer 16, a conventional free layer 18, and a conventional capping layer 20. The conventional pinned layer 14 and the conventional free layer 18 are ferromagnetic. The ferromagnetic layers 14 and 18 typically include materials from the group of Ni, Co, and Fe and their alloys, such as CoFe, CoFeNi, a low-moment ferromagnetic materials. For example materials such as FeCoB, with B from five through thirty atomic percent are used. Although depicted as simple (single) layers, the pinned layer 14 and free layer 18 may include multiple layers. For example, the pinned layer 14 and/or the free layer 18 may include two ferromagnetic layers antiferromagnetically coupled through a thin Ru layer via RKKY exchange interaction—forming a synthetic antiferromagnetic (SAF) layer. For example, a layer of CoFeB separated by a thin layer of Ru may be used for the conventional pinned layer 14 and/or the conventional free layer 18. The thin layer of Ru may, for example be between three and eight Angstroms thick. The conventional free layer 18 is typically thinner than the conventional pinned layer 14, and has a changeable magnetization 19. The saturation magnetization of the conventional free layer 18 is typically adjusted between four hundred and one thousand four hundred emu/cm3 by varying the composition of elements. The magnetization 15 of the conventional pinned layer 14 is fixed, or pinned, in a particular direction, typically by an exchange-bias interaction with the AFM layer 12.
In order to use the conventional MTJ 10 in certain applications, such as in a HDD, a signal that is large in comparison to external field variations is desired. Thus, a high magnetoresistance is also desirable. For HDD applications, a low RA is also desirable. The low RA is considered to be critical in both reducing noise and allowing an impedance match of the conventional MTJ to an external sense amplifier (not shown) in the read head (not shown). Similarly, in MRAM application in which spin transfer based switching is used, a high magnetoresistance is desirable. A large magnetoresistance, which corresponds to a large spin polarization factor, aids in a reduction of the required current density, Jc, for spin transfer based switching. The reduction of spin transfer switching current density Jc is considered critical for making spin transfer switching of a MTJ element applicable in high density MRAM application. An improved magnetic performance will also benefit process control of switching current distribution.
Such a combination of a high magnetoresistance and a low RA has been achieved in conventional MTJs that use MgO as the conventional barrier layer 16. For example, it has been shown that a magnetoresistance (AR/R) of 150% with an RA as low as 3 Ωμm2 can be realized for such a conventional MTJ 10 that uses an MgO for the conventional barrier layer 16 in combination with CoFeB for the conventional free layer 18. Consequently, conventional MTJs 10 that utilize MgO as the conventional barrier layer 16 in combination with CoFeB as the conventional free layer 18 may be used in various device applications.
Although it may be possible to attain a high signal and low RA using the above-described conventional MTJ 10, one of ordinary skill in the art will recognize that such a conventional MTJ 10 has other drawbacks. In particular, the free layer 18 of such a conventional MTJ 10 utilizes an amorphous magnetic layer of CoFeB, with B between zero and thirty atomic percent. However, amorphous layers of CoFeB exhibit a large magnetostriction. This magnetostriction results in poor soft magnetic performance of the conventional free layer 18, making the conventional MTJ 10 unsuitable for use in MRAM applications as well as in HDD applications.
In order to address this issue, a conventional free layer 18 using a multilayer of CoFeB and NiFe has been implemented. The NiFe layer improves the soft magnetic performance of the conventional free layer 18. However the use of such a multilayer for the conventional free layer 18 reduces signal achievable by a significant amount. In particular, an anneal at a temperature of approximately at least three hundred degrees Celsius is generally performed to orient the CoFeB layer to a (100) direction and, therefore, obtain a high magnetoresistance. However, an anneal at these temperatures causes growth of the CoFeB layer in an fcc (111) orientation because of the (111) preference of the NiFe layer. This change in orientation of the CoFeB layer results in a lower magnetoresistance. This low magnetoresistance is a disadvantage that reduces the applicability of such conventional MTJs 10 into ultra-high density HDD and MRAM applications.
Accordingly, what is needed is a system and method for providing a magnetic element that may be utilized in high density HDD and/or other applications. More particularly, a magnetic element that may be used in MRAM applications, particularly those utilizing spin transfer based switching, is desired. The system and method address such a need.